How to Repair Code U110B on a 2009 Mercedes E350

A U110B error code on a 2009 Mercedes E350 indicates a communication issue between control modules, often related to the CAN (Controller Area Network) bus system. This guide walks you through the steps to diagnose and fix the problem.

1. Common Causes of Code U110B

✔ Faulty or loose wiring connections in the CAN bus system ✔ Malfunctioning control module (e.g., ECU, TCU, or ABS module) ✔ Blown fuse or relay affecting module communication ✔ Low battery voltage or weak ground connections ✔ Corroded or damaged connectors ✔ Software or firmware issues requiring an update

2. Tools and Materials Needed

✔ OBD-II scanner with Mercedes-Benz-specific diagnostics ✔ Multimeter for testing electrical continuity ✔ Wiring diagram for the CAN bus system ✔ Screwdrivers and socket set ✔ Electrical contact cleaner ✔ Replacement fuses or relays (if needed) ✔ Battery charger or jumper pack (if voltage is low)

3. Step-by-Step Guide to Repair Code U110B

Step 1: Perform a Diagnostic Scan

✔ Use an OBD-II scanner to retrieve fault codes. ✔ Check for additional error codes that may indicate related issues. ✔ Note any module communication failures reported.

Step 2: Inspect and Test the Battery

✔ Ensure the battery voltage is at least 12.6V with the engine off and 13.7-14.7V while running. ✔ If the voltage is low, charge or replace the battery. ✔ Check for corrosion on battery terminals and clean if necessary.

Step 3: Check CAN Bus Wiring and Connectors

✔ Inspect wiring harnesses for damage, fraying, or loose connections. ✔ Disconnect and clean connectors using electrical contact cleaner. ✔ Check ground connections and tighten any loose bolts. ✔ Test continuity in the CAN bus wiring with a multimeter.

Step 4: Check Fuses and Relays

✔ Locate the fuse box (usually under the hood or dashboard). ✔ Identify fuses related to the ECU, TCU, or other control modules. ✔ Replace any blown fuses and test relays for proper function.

Step 5: Reset the Control Modules

✔ Disconnect the negative battery terminal for 10-15 minutes. ✔ Reconnect the battery and clear the U110B code using the OBD-II scanner. ✔ Start the vehicle and monitor if the code returns.

Step 6: Update Control Module Software (If Needed)

✔ Some communication errors are fixed with software updates. ✔ Check with a Mercedes-Benz dealership or use STAR Diagnostic Tool for updates. ✔ If an update is available, install it to resolve the issue.

4. Troubleshooting Persistent U110B Code Issues

Issue: Code Reappears After Clearing

✔ Check for hidden CAN bus faults using an advanced Mercedes-Benz scanner. ✔ Test communication at each control module individually. ✔ Consider replacing the affected module if other fixes don’t work.

Issue: Other Electrical Problems Appear

✔ Inspect the voltage regulator and alternator for inconsistencies. ✔ Verify that all wiring harnesses are intact and properly connected.

Issue: Dashboard Warning Lights Stay On

✔ Some control modules need a hard reset via a professional diagnostic tool. ✔ Visit a certified Mercedes-Benz technician for further diagnostics.

5. Final Thoughts

A U110B code on a 2009 Mercedes E350 often points to wiring, battery, or module communication issues. Systematic troubleshooting using an OBD-II scanner, wiring checks, and software updates will help restore proper function. If issues persist, consulting a Mercedes-Benz specialist may be necessary.

Frequently Asked Questions (FAQs)

Can I drive with a U110B code?

✔ It’s not recommended, as module communication failures can lead to safety issues.

How much does it cost to fix a U110B code?

✔ DIY repairs cost $0-$50 (if cleaning connections or replacing fuses). ✔ Professional diagnostics and module repairs range from $100-$500+.

Can a weak battery trigger a U110B code?

✔ Yes, low voltage can disrupt module communication. Always check battery health first.

By following this guide, you can diagnose and fix code U110B on your 2009 Mercedes E350, ensuring proper vehicle operation and avoiding unnecessary repair costs.